The present invention relates to novel electrically conductive polymer complexes, electrically conductive resists, uses thereof and structures fabricated therewith. More particularly, this invention relates to water-soluble, electrically conductive substituted and unsubstituted polymer complexes and their use as, inter alia, electrical discharge layers, resists, discharge layers for electron-beam lithography and SEM (scanning electron microscope) inspection, and as coatings (especially radiation-curable coatings), for electrostatic charge (ESC) and electrostatic discharge (ESD) applications.
In electron-beam lithography using organic resists, which are insulators, there can arise an accumulation of charge during the writing process due to the absence of an adequate conducting path for immediate bleed-off of the electrons. This charging can result in beam pattern displacement deflection, loss of accuracy in pattern-to-pattern-overlay, or in extreme cases a catastrophic discharge of voltage.
Traditionally, suggestions to circumvent this problem have included the use of a discharge layer in the form of a conductor below or above the resist coating. The layer could be in the form of thin evaporated or sputtered metal coatings, indium-tin oxide films, or amorphous carbon films produced by chemical vapor deposition processes. Although effective in some contexts, these methods are not universally ideal since the processes involved in their utilization tend to influence negatively the performance of the resist, and in some cases are difficult to remove.
It is also useful to provide materials that can alleviate electrostatic charging (that is, the unwanted accumulation of static electricity which becomes capable of attracting unwanted airborne particles to e.g. cathode ray tube screens and electronic component carriers), and alleviate electrostatic discharge, in which static electricity is suddenly released in a discharge that can distort the performance of electronic devices and even damage or destroy electronic components. A material that can facilitate the application and creation of such materials would be useful.
While polyaniline as described in the literature might be considered a promising candidate to use to solve these needs, the practical use of currently available polyaniline-based systems has been limited due to the fact that solvents such as N-methyl pyrrolidinone are needed for the application and removal. These solvents are known to interfere with some substrate chemistries. In addition, they create interfacial problems and can tend to dissolve certain substrates. Still other selective polyaniline-derived systems are soluble in more benign organic solvents; however, they are known to be difficult to remove once applied. It is also useful to form a conducting resist which provides patterns of conductive lines on a substrate. The steps involved in forming such lines can include depositing a layer, exposing selected portions of the layer to a given radiation (e.g., ultraviolet or visible light, electron beam, X-ray, or ion beam) to create a solubility difference between exposed and unexposed portions, and then removing the more soluble portions so that only the desired pattern remains. This type of technique is often frustrated by the difficulty of removing the unwanted material after it is developed.
The problem of charging in electron-beam methods arise because the resists are insulators. With a conducting resist, which is one aspect of the present invention, charging should not occur and a separate discharge layer should not be needed.
Thus, there remains a need for a polymeric material which can be used in the applications described herein, and which is easily applicable; is chemically inert with respect to the systems with which it is used; is environmentally benign, particularly in not requiring the use of organic solvents which would volatilize into the atmosphere; and which is removable when desired with minimal effort, with minimal harm to the substrate itself.
The preparation of polyaniline systems is described in Li et al., xe2x80x9cSoluble Polyanilinexe2x80x9d in Synthetic Metals, 20 (1987), at pages 141-149. That article discloses that, even when the polymerization of the aniline is carried out in the presence of the polyacid polystyrene sulfonic acid (PSSA), the polymerization results in a precipitate from the aqueous solution in which the aniline polymerization proceeds.
MacDiarmid et al., in xe2x80x9cPolyaniline: A New Concept in Conducting Polymersxe2x80x9d, Synthetic Metals, 18 (1987), at pages 285-290, describe polyaniline and its protonated form, and indicate that the material is electrically conductive.
U.S. Pat. No. 5,068,060 relates to the synthesis of poly(heterocyclic vinylenes) as electrically conductive materials. According to the disclosure, the backbone of the polymer is altered to impart desired properties, and solubility is exhibited only in an undoped precursor form. U.S. Pat. No. 4,929,389 and U.S. Pat. No. 4,880,508 relate to the synthesis of water soluble conductive polymers, in which the moiety responsible for water solubility is incorporated into the backbone of the polymer. By contrast, in the present invention the final product exhibits both water solubility and electrical conductivity, and does so without requiring alteration of the polymer backbone.
U.S. Pat. No. 4,375,427 relates to the synthesis of thermoplastic-type polymers that can be doped to be made conductive. However, the disclosed materials are not water soluble, and are synthesized by condensation reactions rather than oxidation reactions.
One aspect of the present invention resides in a water-soluble electrically conductive composition of matter comprising a polyacid and a polymer comprising at least one conjugated region composed of repeating units incorporating a conjugated basic atom. A preferred example of such a repeating monomeric unit is aniline or a substituted aniline, which incorporates a nitrogen atom in that the nitrogen can participate in the conjugation in the polymer.
Another aspect of the present invention comprises solutions, in particular agueous solutions, of such compositions of matter.
Another aspect of the present invention comprises a process for forming a water-soluble, electrically conductive composition of matter comprising a polyacid and a polymer, such as polyaniline, comprising at least one conjugated region composed of monomeric units incorporating a conjugated basic atom. The process comprises forming a solution of said polyacid and the corresponding monomer, wherein the number of acid groups in the polyacid exceeds the number of protonatable basic atoms in the polymer to be formed (it being understood that the polymer will include basic atoms that are not protonatable), and polymerizing the monomer while controlling the rate of initiation and the rate of propagation of said polymerization such that the polymerization forms said water-soluble composition of matter.
Further aspects of the invention includes compositions of matter which are water-soluble and electrically conductive as described herein and which are cross-linkable upon exposure to electromagnetic radiation to form water-insoluble conductive products; structures having such a composition of matter disposed thereon; processes of using such compositions of matter to make electrically conductive layers and films; and the products formed by such cross-linking, such as conducting resists.
Yet another aspect of the present invention is a structure, comprising a substrate on which is disposed said water-soluble electrically conductive composition of matter. Such structures include dielectric materials; said composition of matter is useful as a conductive electron beam resist, optical resist, X-ray resist, and electrostatic discharge layer.
A further aspect of the present invention comprises a method of disposing said water-soluble, electrically conductive composition of matter on a surface as e.g. a conductive resist or an electrostatic discharge layer.